1. Field of Invention
The present invention relates to mortise locks and, more particularly, to a latch assembly for mortise locks.
2. Related Prior Art
Referring to FIG. 5, a mortise lock latch assembly in accordance with prior art has a box-shaped frame 40 which is generally securely attached to a lock stile of a door (not shown). The box-shaped frame 40 essentially consists of two parallel plates 42 each having a slot 44. A cylinder 46 has a circumferential slot 48. A ring 50 from which a finger 52 extends is sited in the slot 48. A core 54 is inserted through the cylinder 46 and the ring 50. The finger 52 is moved along the slot 48 when the ring 50 is rotated by the core 54 when activated by a key (not shown).
A dead bolt 56 has two separated parallel plates 58. Each plate 58 has (A) two cutouts in an edge so as to form shoulders 60 and 62 and a tab 64 sited between the shoulders 60 and 62, (B) a hole 66 defined near an opposite edge, (C) a slot 68 extending parallel to the edge wherein the cutouts are formed, (D) a hole 70 defined near a closed end of the slot 68, (E) a channel 72 extending through the hole 66. The channels 72 of the plates 58 constitute a passage for a spring 74.
A plate 76 has a first portion 78, a second portion 80 transversely extending from the first portion and a third portion 82 transversely extending from the second portion 80. The second portion 80 contains a longitudinal slot 84. Two teeth 86 transversely extend toward the first portion 78 from the third portion 82. Two separated strips 88 transversely extend from the third portion 82.
The plate 76 is sited between the plates 58 and a pin 90 is inserted through the holes 70 and the slot 84, thus the dead bolt 56 is attached to the plate 76. The spring 74 is inserted through the passage and retained between the strips 88. A pin 92 is inserted through the holes 66. The spring 74 is compressed between the third portion 82 and the pin 92. A pin 94 is inserted through the slots 68 and the space between the first and third portions 78 and 82. Two ends of the pin 94 are secured in two holes defined in the plates 58.
Referring to FIG. 6, the core 54 is activated in order to rotate the finger 52. The finger 52 is moved so that it presses the strip 76 and simultaneously compresses the spring 74. As being further rotated, the finger 52 abuts the shoulder 60 and moves the dead bolt 56 out of the box-shaped frame 40. The finger 52 is disengaged from the shoulder 60 when it is further rotated. That position is shown by a dashed line in FIG. 7. Obviously, after a revolution of the finger 52 is completed, a sufficient amount of the extension of the dead bolt 56 out of the box-shaped frame 40 for locking a door is not achieved as a clearance exists between the door and a jamb wherein a bolt-receiving hole is formed (not shown).
Referring to FIG. 8, the finger 52 continues to be rotated. The finger 52 presses the strip 76. The finger 52 abuts the tab 64. The finger moves the dead bolt 56 out of the box-shaped frame 40 by abutting the tab 64. Then, the finger 52 is disengaged from the tab 64.
A first problem of the above-mentioned mortise lock latch assembly is that the key must be rotated for at least two revolutions to lock the door. Generally, the key is rotated for 720.degree. to move the dead bolt about 18 mm.
A second problem of the above-mentioned mortise lock latch assembly is that there is a position where the finger 52 is disengaged from the tab 64 and the strip 76 is not biased by means of the spring 74 to have the pin 94 sited between the teeth 86. If the bolt-receiving hole is blocked on purpose, the strip 76 will be stopped in such a position. The dead bolt 56 can be easily moved into the box-shaped frame by inserting a strong strip between the box-shaped frame and the jamb.
Therefore, the present invention is intended to solve the above-mentioned problems.